When a gas well is stimulated, the initial raw gas emitted at the wellhead is a mixture of natural gas, other hydrocarbons and contaminates, such as hydrogen sulfide (H2S), water (H2O) and carbon dioxide (CO2). This so-called “dirty” gas may also contain particulate matter, such as sand and particles of drilling fluids.
Each pipeline company has its own set of natural gas quality specifications that delivered gas must meet. For example, pipelines typically limit CO2 content due to its corrosive properties. A common maximum for CO2 content in delivered is gas is one to three percent (1-3%) by volume, while raw gas from a recently stimulated well may exceed 30 percent. Similarly, hydrogen sulfide is corrosive and is hazardous to humans if inhaled, so it is also subject to restrictions (typically ≦4 ppm) by pipeline companies. In addition, delivered gas specifications typically limit water vapor content.
Because of these common contaminants, raw gas produced immediately after stimulation rarely meets typical delivered gas specifications. However, in most wells, the gas stream will soon become pipeline quality if the well is flared or vented for a brief period. For example, most gas wells begin producing marketable gas after 3-5 days of flaring. The dirty gas usually is vented to the atmosphere until sensors show reduced and acceptable levels of contaminants.
Flaring has a detrimental effect on the environment because it releases the contaminants into the air. In addition, flaring wastes a significant amount of natural gas and other hydrocarbons. For example, when raw gas containing five percent (5%) contaminants is flared, ninety-five percent (95%) of the flared product is good natural gas that is wasted. Treatment and sale of the dirty gas would significantly increase profits to operators, tax revenues to the states, and payments to the royalty owners.
Permanent and semi-permanent treatment systems have been used at well sites where the deep gas is not pipeline quality and permanent treatment of the produced gas is required. Alternately, produced gas from such wells has been shipped to processing facilities remote from the well. Neither of these options is economically feasible for cleaning the gas produced after a stimulation procedure in a well where only the initial post-stimulation gas is unmarketable.
The present invention provides a mobile gas separation system suitable for temporary use at the well site of a recently stimulated gas well. The system is adequate to serve wells with a range of different requirements. The method of this invention permits the sequential use of the gas separation system for short periods of time at a number of wells, each having different capacities and requirements. Accordingly, the method and system of this invention provide a temporary, on-site cleaning of dirty gas, preserving this valuable natural resource, protecting the environment, and maximizing revenues to the state, the operators and the royalty owners.